As a cooling apparatus for a heat-generating element, there is known an apparatus which comprises a heat sink configured such that the heat-generating element is mounted on one surface of the heat sink and the generated heat is radiated from the other surface. For example, a cooling apparatus for a heat-generating element is disclosed which employs a direct cooling system configured such that a cooling component having a recess is arranged to face the heat sink and a coolant is made to flow in a coolant passage formed by the recess of the cooling component, thereby cooling the heat sink (Japanese Patent Application Publication No. 2007-250918 A).
In Japanese Patent Application Publication No. 2007-250918 A, a coating film is formed on the surface of the heat sink to prevent corrosion of the heat sink. Accordingly, there is a disadvantage in cost.
In the cooling apparatus for a heat-generating element using the above-described direct cooling system, when the sealing member is provided to seal between the heat sink and the cooling component, a small gap is formed between facing surfaces of the heat sink and the cooling component at the interior side of the coolant passage near the sealing position. In this case, the, coolant will stay in this gap and the staying of the coolant causes corrosion of the heat sink and the cooling component by the following reason. First, when the coolant stays in the above gap, the concentration of dissolved oxygen is constant in the coolant staying there. On the other hand, the concentration of dissolved oxygen will increase in the coolant flowing through other passes in the coolant passage because oxygen dissolves into the coolant while the coolant passes through components, such as a pump, which are connected with the cooling component in order to push out the coolant. This will cause a difference in the concentration of the dissolved oxygen in the coolant. If a difference in the concentration of the dissolved oxygen occurs, a concentration cell will be formed on the surface of the heat sink to cause local corrosion (crevice corrosion) of the heat sink. Moreover, as the local corrosion of the heat sink progresses, the pH of the coolant is lowered due to effect of metal ions dissolved from the heat sink, and the cooling component is also corroded. If the heat sink is dissolved and the cooling component is corroded, a plating layer or the like formed on a surface of the heat sink and/or of the cooling component will be delaminated. The delamination of the plating layer or the like causes the liquid leakage from the sealing position. In such a situation, Japanese Patent Application Publication No. 2007-250918 A has a disadvantage in cost because a coating film may have to be formed on the surface of the heat sink to prevent corrosion of the heat sink and the cooling component.